Light speed and gravitational matrix

Light appears to travel at a constant velocity in a constant medium/matrix. According to Einstein, gravity is the opposing force of displaced space/time matrix by mass. The more mass, the more the gravitational displacement.

Light is "bent" around massive objects.

Shapiro? says there is a "time lag" of light passing around massive objects.

Questions:

Why did the propagation of light in a matrix theory die?

Why can't the propagation matrix be the same gravitational matrix?

Why can't the time lag be accounted for by the slowing of light in a denser matrix?